Contamination Analyses of ISS Vehicle Visits

The SAGE III Contamination Monitoring Package detects the contamination environment in the immediate vicinity of the payload using eight Thermoelectric Quartz Crystal Microbalance sensors that telemeter continuous beat frequency measurements to the ground. The single greatest source of contamination measured to date was the SpaceX Cargo Dragon, whose outgassed contaminants chemisorbed to the gold electrodes of the sensors. This paper contains results from the mission’s first three years, including the signals observed from every visible visiting vehicle, the measured effects on the overall payload, and learned lessons to consider for future ISS or TQCM missions.

Quantum Study of Symmetrical/asymmetrical Chare/Energy Transfer in a Simple Candidate Molecular Switch

Based on molecular nanoelectronic knowledge, field-effect molecular electronic devices can be designed for use in nano-circuits. Therefore, in this study, a candidate field-effect molecular switch (isolated, M, and non-isolated, Au-M-Au/Au4-M-Au4, molecular systems) is studied, using density function/pseudopotential model (DFT/LANL2DZ). This molecular switch's switching mechanism (ON/OFF) we performed by applying an external electric field-effect. In this regard, some computational studies related to this molecular switch's electronic/vibrational transfer properties were investigated. Also, used from the quantum theory of atoms in the molecule (QTAIM), Landauer's theory (LT), and energy/charge transfer mechanisms were used at the atomic scale to predict this molecular switch's voltage-current (IV) behavior. Analysis of these results showed that when the intensity of the applied electric field increases to 0.008 au, the molecular switch is in the ON state. In addition, the role of gold electrodes on some of the electronic/vibrational properties of this molecular switch was investigated. Analysis of the results showed that gold electrodes play an essential role in the local distribution of charge and intramolecular energy and, consequently, the I/V diagram of this molecular switch. It is expected that such quantum-based research (without using numerical methods such as Green's function methods) could open new horizons in the quantum study of molecular parts at the atomic-intramolecular scale.

Electrochemical nano-roughening of gold microstructured electrodes for the enhanced detection of copper and glucose

One of the main challenges for electrochemical sensor miniaturization is the fabrication of electrodes with a smaller footprint, while maintaining, or even increasing, their sensitivity for the targeted application. Our research group has previously demonstrated the enhancement of the electroactive surface area of gold electrodes up to 6-fold, relative to planar gold electrodes with the same footprint, through the generation of a wrinkled thin film surface via thermal shrinking. In this work, the electroactive surface area of wrinkled gold electrodes was further enhanced up to 5-fold (30-fold over flat electrodes) using a chronoamperometric pulsing technique. Scanning electron microscopy images showed progressive increase of surface roughness in response to an increasing number of applied pulses. The resulting nanoroughened electrodes present several advantages in addition to the enhanced electroactive surface area. These electrodes offer superior fouling resistance compared to that of wrinkled and flat electrodes when submerged in a solution containing bovine serum albumin at high concentrations. Cyclic voltammetry data also revealed greater sensitivity of nanoroughened electrodes toward anodic copper stripping, where the limit of quantification of copper by the nano-roughened electrodes was 0.3 ppm. Nano-roughened electrodes also allowed the highly sensitive enzyme-free detection of glucose through chronoamperometry, with a limit of detection of 0.5 mM, whereas planar electrodes did not demonstrate any ability to oxidize glucose. We foresee that this methodology to fabricate nanostructured electrodes will accelerate the development of simple, cost-effective and high sensitivity electrochemical platforms.